Method for separating layers from articles

ABSTRACT

A method for separating layers from articles made of high-speed steel and having at least one layer of TiAlN, includes applying an alkaline solution containing hydrogen peroxide, a base as well as acid to the layer. The acid is selected from phosphates, phosphonates and phosphonic acids.

This is a national stage of PCT Application No. PCT/CH98/00479, filedNov. 9, 1998, and now pending.

FIELD AND BACKGROUND OF THE INVENTION

The present invention relates to a method for separating layers fromarticles provided with a hard material layer comprising a Ti compound,in an alkaline solution comprising

hydrogen peroxide

at least one base

at least one acid and/or a salt of an acid.

DD 228 977 describes a method for separating of TiN layers, inparticular for separating TiN layers applied onto nickel substrates. Thearticles to be treated are therein placed into a hydrogen peroxidesolution with a content of 35 Ma % peroxide for approximately 3 minutesat a temperature of approximately 70° C. to 80° C., subsequently rinsedin water, dried and then mull-wiped off. For the separating of TiAlNlayers, this method is unsuitable, since TiAlN is poorly soluble inhydrogen peroxide solution.

According to GB 2 127 042 titanium nitride hard material layers onsubstrates of stainless steel are separated in aqueous nitric acid attemperatures above 70° C. The layer separation time for a 1 μm thicklayer at 70° C. is approximately 50 hours. This extremely long layerseparation time is of great disadvantage.

A method for the layer separation of hard material layers on differentmetal substrates is known from U.S. Pat. No. 4,746,369. The acidic layerseparation bath is composed of hydrogen peroxide as oxidant and aphosphoric acid or nitric acid. Further, different surface-activematerials are used. The very low pH value of the solution of less than0.5 is of disadvantage for the application on high-speedsteel-substrate-HSS (High Speed Steel).

DE 41 10 595 proposes to carry out hard material layer [separation] fromtool surfaces in a hydrogen peroxide solution stabilized by complexingagents with potassium sodium tartrate ttrahydrate or sodium gluconatebeing used as the complexing agent. On the one hand, TiAlN layers arethereby not separated at a satisfactory rate and, on the other hand, thestabilizers used exhibit only a conditionally stabilizing effect.

From DE 41 01 843 a method is known for the layer separating of objectslayered with hard material layers, wherein the objects are treated witha solution comprising tetrasodium diphosphate and hydrogen peroxide.Typical are hydrogen peroxide concentrations of 8 to 12%, the relativelyhigh tetrasodium diphosphate concentration of 8 to 12%, high processtemperature at boiling temperature, and high pH values of 8 to 12. Ifthe solution is concentrated by evaporation—which occurs relativelyrapidly at the high temperatures—phosphatization of the alreadydelayered surface can occur. Titanium nitride and/or titaniumnitride/carbide hard material layers are separated.

Lastly, from DE 43 39 502 methods are known which are specific to thelayer material, for the layer separating of metal substrates, inparticular also of hard metal substrates, which comprise hard materiallayers comprised of either TiN, TiCN or TiAlN or of layer systemscomprising TiN/TiAlN.

Therein an alkaline solution with hydrogen peroxide, at least one baseas well as at least one salt of mono- and dicarboxylic acids is used.

Depending on the layer to be separated, and while protecting thesubstrate, the solution bath is composed of a multiplicity ofcomponents, specific to the layer material.

SUMMARY OF THE INVENTION

Building on the last-cited method specific to the layer material, it isthe task of the present invention to propose a method with whichsignificantly simpler and more flexibly large-scale industrialhigh-speed steel substrates can be delayered, and specificallyindependently of whether or not they are layered with a TiN, a TiCNand/or a TiAlN hard material layer. In contrast to the above describedmethod, according to the invention one and the same method becomespossible for the separation of all cited hard material layers from HSSsubstrates.

Definitions

1) High-Speed Steel

A high-speed steel is characterized by high carbon concentrations of upto 1.5%, and additions of strongly carbide-forming elements such aschromium, molybdenum, tungsten and vanadium. Up to 12% of cobalt iscomprised in some of the more complex grades.

This steel is referred to as high-speed steel because it retains itshigh hardness at high-speed applications (see D. T. Llewellyn, Steel:Metallurgy and Application, Butterworth-Heihemann Ltd., Oxford 1992, p.174).

2) Phosphate

As a phosphate is defined a salt of a phosphoric acid, diphosphoricacid, triphosphoric acid, etc. For example, the phosphate “calciumphosphate” is a salt of phosphoric acid, “disodium dihydrogen phosphate”is a salt of diphosphoric acid, further “pentasodium triphosphate” is asalt of triphosphoric acid.

3) Phosphonate

By a phosphonate is understood a salt of a phosphonic acid, inparticular of an organic phosphonic acid, i.e. of a phosphonic acid withorganic substituents.

The posed task is solved thereby that for the layer separation of HSSsubstrates with at least one layer comprising TiN, TiCN or TiAlN, atleast one substance from the group of phophates, phosphonates andphosphonic acids is used.

Preferably the following specific method guidances are usedalternatively or in combination:

the phosphate disodium dihydrogen pyrophosphate, Na₂H₂P₂O₇ and/orpentasodium triphosphate (Na₅P₃O₁₀) are preferably used;

as the phosphonic acid is preferably used aminotri(methylene phosphonicacid) and/or 1-hydroxyethane (1, 1-diphosphonic acid). These phosphonicacids are added to the solution as such. This applies generally to theuse of phosphonates, phosphates and phosphonic acids.

It has been found, at least preliminarily, that the use of 1-hydroxyethane(1, 1-diphosphonic acid) is especially suitable.

The process temperature of the solution bath is maintained at 20° C. to80° C. (the range limits are included), if appropriate by heating and/orcooling;

The peroxide concentration is s elected between 5 and 50 wt. % (therange limits are included);

The concentration of phosphate and/or phosphonate and/or phosphonic acidis selected between 0.1 and 10 wt. % (the range limits are included);

Relatively large solution bath volumes, for example ≧50 l or even ≧100 1can also be stably operated;

The solution comprises preferably distilled water, hydrogen peroxide,the cited base, for example NaOH, and the cited phosphates and/orphosphonates and/or phosphonic acids, at least by a far predominantfraction.

This permits circumventing a layer material-specific and complexsolution composition and the feasibility is created of separating layersof each of the listed hard material layers from HSS substrates with thesame solution. Furthermore, the extremely high apparatus expenditure isdispensed with, which must be expended if an alkaline hydrogen peroxidebath with a pH value of 8 to 12 is operated in the boiling temperaturerange. Due to the low process temperature at which the solution bathaccording to the invention can be operated, the danger ofphosphatization is also absent, which exists at high processtemperatures in the boiling temperature range due to rapid concentrationthrough evaporation.

This offers the capability for economic and large-scale industrial layerseparation to operate stably delayering baths with large volumes, forexample of more than 50 l or even of more than 100 l . Therewith largequantities of hard-material layered HSS substrates, such as for exampletools, can be delayered within a few hours.

In contrast to TiN and TiCN, TiAlN does not dissolve in hydrogenperoxide solutions even at increased temperatures. If the pH value ofthe hydrogen peroxide solution is raised by adding a base, such as NaOH,into the alkaline range with a pH≧7, in addition to the cited TiN andTiCN layers, TiAlN layers are also dissolved. It was found according tothe invention that this is also the case at low process temperatures.

An advantage of the alkaline hydrogen peroxide is the high processcertainty with respect to corrosion of HSS material. In an alkalinemedium HSS is highly inert. Thus, no corrosion danger for the HSSsubstrate exists even if relatively long layer separation times wouldhave to be used.

The problem of instability of alkaline hydrogen peroxide solutions, inthat an autooxidation of the hydrogen peroxide occurs which is catalyzedby metal ions which are released into the solution during the delayeringprocess, which in turn leads to overheating and boiling-up of thedelayering bath, is solved according to the invention through theaddition of at least one phosphate and/or phosphonate and/or at leastone phosphonic acid as stabilizer. Through this addition the layerseparating is furthermore accelerated, and specifically with respect toall cited hard material layers. Through this addition the bath stabilityis improved such that the layer separation bath could be stably operatedeven at increased temperature. For maintaining the bath temperature, aheating and/or cooling system can be provided; if appropriate the bathtemperature is regulated to a nominal value, with the heating and/orcooling system as the correcting element.

DESCRIPTION THE PREFERRED EMBODIMENTS

Regarding the differences in efficacy of phosphates and/or phosphonatesand/or of phosphonic acid in the solution used according to theinvention:

When using phosphate alone the bath service life is relatively modest,in the normal case it is between 1 and 3 charges, which, it isunderstood, is quite sufficient in certain cases. This relatively modestbath service life is due to the restricted stability of polyphosphates.The stability of polyphosphates in alkaline solutions is only moderate,in acidic solutions it is poor. Through hydrolysis the polyphosphatesare converted to orthophosphates which are far less effective for thestabilization of the peroxide solutions.

In the case of organic phosphonates and phosphonic acids the behavior isdifferent.

In comparison to the inorganic polyphosphates, phosphonates andphosphonic acids have very good hydrolytic stability. This can be tracedback to the very high stability of the C—P bonds of the phosphonates andphosphonic acids. In addition to the increased stabilizing effect,increase of the bath service life, phosphonates and phosphonic acidslead, furthermore, to a further acceleration of the layer separationreaction.

EXAMPLE I

The following solution was used as the layer separation bath:

125 l hydrogen peroxide, 17.5 wt. %

1.25 kg Na₅P₃O₁₀

500 g NaOH.

The bath was heated to 60° C. and 500 pieces of 12 mm HSS end-millingcutters, layered with a TiAlN layer, were placed into the solution. Thetools were completely delayered after 3 hours and the bath temperaturehad remained stable at 60±2° C.

EXAMPLE II

The following layer-separation solution was prepared:

125 l hydrogen peroxide, 17.5 wt. %

0.2 mol/l aminotri-(methylene phosphonic acid) ATMP

0.4 mol/l NaOH

The temperature of the layer-separation solution was kept constant atapproximately 60° C. through heating/cooling and 500 pieces of 12 mm HSSend-milling cutters layered with a TiAlN layer were placed into thesolution. The tools were completely delayered after three hours and thebath temperature had therein stayed stably at 60±2° C. It was possibleto separate the layers of the cited charges in the same solution.Compared to the use of polyphosphates according to Example I, the bathservice life could be extending by a factor of 2 to 4.

EXAMPLE III

The following layer separation solution was prepared:

125 l hydrogen peroxide, 17.5 wt. %

2 wt. % 1 -hydroxyethane (1,1-diphosphonic acid) HEDP

0.4 mol/l NaOH.

Operated and charged as in Example II, however with shortened delayeringtimes, the same results were obtained as in Example II.

One advantage of the present invention is the simple solutioncomposition, the simple process guidance and the short layer separationtime. At solution temperatures markedly below the boiling point, it ispossible to obtain already within a few hours the separation of thelayers. With respect to corrosion on HSS substrates high certaintyexists: no corrosion of HSS takes place since the delayering solution isalkaline.

An essential advantage is further that in the same pass, i.e. with thesame layer-separation solution a large number of HSS substrates, forexample mixed with TiN, TiCN and/or TiAlN layers, can be delayered interalia thereby that high volumes of solution, for example of more than 50l or even of more than 100 l , can be stably operated with lowexpenditure.

What is claimed is:
 1. A method of separating at least one hard materiallayer from a high-speed steel substrate of an article, comprising:providing an article having at least one hard material layer comprisingTiAlN; and exposing the article to an alkaline solution containinghydrogen peroxide, at least one base, and at least one of an acid and ofa salt of an acid, the at least one of said acid and of said salt of anacid comprising at least one substance selected from the groupconsisting of phosphates, phosphonates, and phosphonic acids.
 2. Amethod as claimed in claim 1, including adding phosphonate to thesolution to provide the at least one acid.
 3. A method as claimed inclaim 1, including adding an organic phosphonic acid to the solution oprovide the at least one acid.
 4. A method as claimed in claim 1,wherein the at least one acid is selected from the group consisting of:phosphonic acid, aminotri-(methylene phosphonic acid) and1-hydroxyethane(1,1-diphosphonic acid).
 5. A method as claimed in claim1, wherein the phosphate is at least one of disodiumdihydrogenpyrophosphate and Na₂H₂P₂O₇ and pentasodium triphosphate(Na₅P₃O₁₀).
 6. A method as claimed in claim 1, including maintaining thesolution at a temperature of about between 20° C. and 80° C.
 7. A methodas claimed in claim 1, wherein the hydrogen peroxide has a concentrationof between about 5 and 50 wt. %.
 8. A method as claimed in claim 1,wherein the concentration of at least one of phosphate and phosphonateand phosphonic acid is between about 0.1 and 10 wt. %.
 9. A method asclaimed in claim 1, wherein a solution volume of at least 50 l is used.10. A method as claimed in claim 1, herein a solution volume of at least100 l is used.
 11. A method as claimed in claim 1, wherein,simultaneously, in addition to at least one TiAlN layer, at least one ofa TiN and a TiCN layer is separated from the article.
 12. A method asclaimed in claim 1, wherein the layer is separated from a tool whichcomprises the article.
 13. A method as claimed in claim 12, wherein thelayer is separated from a cutting or forming tool.
 14. A method asclaimed in claim 13, wherein the layer is separated from an end-millingcutter, an indexable insert or a stamping tool.
 15. A method formanufacturing a high-speed steel substrate of an article, comprising:providing an article having at least one hard material layer comprisingTiAlN; and exposing the article to an alkaline solution containinghydrogen peroxide, at least one base, and at least one of an acid and ofa salt of an acid, the at least one of said acid and of said salt of anacid comprising at least one substance selected from the groupconsisting of phosphates, phosphonates, and phosphonic acids.
 16. Amethod as claimed in claim 15, including adding phosphonate to thesolution to provide the at least one acid.
 17. A method as claimed inclaim 15, including adding an organic phosphonic acid to the solution toprovide the at least one acid.
 18. A method as claimed in claim 15,wherein the at least one acid is selected from the group consisting of:phosphonic acid, aminotri-(methylene phosphonic acid) and1-hydroxyethane(1, 1-diphosphonic acid).
 19. A method as claimed inclaim 15, wherein the phosphate is at least one of disodiumdihydrogenpyrophosphate and Na₂H₂P₂O₇ and pentasodium triphosphate(Na₅P₃O₁₀).
 20. A method as claimed in claim 15, including maintainingthe solution at a temperature of about between 20° C. and 80° C.
 21. Amethod as claimed in claim 15, wherein the hydrogen peroxide has aconcentration of between about 5 and 50 wt. %.
 22. A method as claimedin claim 15, wherein the concentration of at least one of phosphate andphosphonate and phosphonic acid is between about 0.1 and 10 wt. %.
 23. Amethod as claimed in claim 15, wherein a solution volume of at least 501 is used.
 24. A method as claimed in claim 15, wherein a solutionvolume of at least 100 1 is used.
 25. A method as claimed in claim 15,wherein, simultaneously, in addition to at least one TiAlN layer, atleast one of a TiN and a TiCN layer is separated from the article.
 26. Amethod as claimed in claim 15, wherein the layer is separated from atool which comprises the article.
 27. A method as claimed in claim 26,wherein the layer is separated from a cutting or forming tool.
 28. Amethod as claimed in claim 27, wherein the layer is separated from anend-milling cutter, an indexable insert or a stamping tool.